Low temperature carbonization of coal



`llne 23, 1942. c, E, LESHER f- TAL 2,287,437

LOW TEMPERATURE CARBONIZATION OF COAL Filed Jan. 26, 1940 INVENTORS CarlEl 65h61 john E.Go0de Peieoie'd June 23,1942 y y y 2,287,437

a UNITED STATES PATENT-OFFICE y ,Y .2,227,431V f un y Low- TEMPERATUREcARBoNTzA'rIoN oF CarlE.kLesher, Ben` von Heights, .and John v Goode,McDonald, Pa., assignors toPitvtsburxh n Coal Carboniz'ation Company,Pittsburgh, a corporation of Delaware Application Januaryzs, 1940, sealNo. 315,118 i 1o crains; (ciauz-fs) This inve tion relates to the lowtemperature for commercial use-or in finely divided' particles'carbonization of coal and particularly to certain which havenocommercial value. This., as we l temperature carbonizationprocessyabove 1re 15 ytion has I existed over a considerable period thecoal is plastic at a temperature not higher yi118 ilQthe interiorf theSteel yShell aS Well as -"One of "the prin vhas been of rundesirablypoorquality Iand has." -frial meets the steel shell of theretort the .teniimprovements in the manufacture of coal balls believehasbeen dueto improper control of by the low temperature vcarbo'nizationprocess. the movement of thecoalthrough the carbone This process is thesubject of Wisner Patents 5 iz'erand-:lackof proper heat treatmentthereof Nos. 1,490,357, 1,748,815 r and 1,756,896 and in thepreheating,.p1astic and` ball-conditioning Lesher Patent-No.2,080,946.Whilethe process zones. y 4 disclosed in osaid patents has provedcommer` `It isvdifiicult for us to assign denite reacially satisfactoryit-has been'found to vhave cer.- sons for the unsatisfactory resultsobtained by tain operating disadvantages which havegreat-l 1o the priorprocess and. we do not assume to 1y reduced the leconomy oftheprocessandhave understand or state `fully all of such reasons. in someinstances adversely aiiected-thequality It is, however, the fact thatsuch process has of the product. 1 not given .uniform resultsand hasnotat yall In the manufacture ofv coal balls ,by the low times-been `fullyysatisfactory and, this condiferred to'iinelydivided coal is ordinarilyYiirst prior to the present.y invention. `The following thermodized orroasted infcontact with air, y explanation represents our present beliefas to which results in partially oxidizing the coal, the reasons for theshortcomings of the prior andthe roasted partial1yoxidizedjcoal is thenprocess. z t preferably maintained ina heated recirculating Certainobservable` facts in .the prior process storage streamffrom which itiswithdrawn, are that iine. coal is heated to 600F..in the mixed withcoke breeze and fed tothe carbon',- presence oi air ,and mixed withIfine coke, also, izer; With certain coals the roasting step: ispreheated tol about. the same temperature; the omitted.' The carbonizermay assume various mixture ischarged into the upper end oany informs andinvone embodiment constitutes an inclined` .revolving steel retort,externally heated clinedrotary retort.r The coal heated to about by,gases rangingdn temperatureffrom 1050" F. 600 F. is introduced intothe,upper'e n'd `of gthe at the lower end of the rertto 850 cr 950 F.retort and'as-the Vretort rotates thevcoall works at the llppel'nd; theS1096 0f 'the :retort and its way downwardly therein. In the retortv the,itsr revolving action convey this mixture of hot coal is firstpreheated-or raised kto a tempera- 30 coal` and cokebreeze along itslength; hydro,- ture approaching its softening temperaturel ors carbongas is discharged at either the upper that at which it :becomes plastic.vUpon further end or ,the-1 lowerA end 0f the retort and 10W heating:the coal becomes plastic, after which temperaturel colte in ball formis `discharged it breaks up andformsv'into lballsvas described at thelower end. ,I y, y, y ,A in the patents abovementioned. :Such ballsWlltakesl P1306 inthe revlvng'tlt in will'be referred to herein :as coallballsT,- al; *,operationis, of course,impossibleofl direct'obthoughthey are of course; constituted by parservation. Wehave madeobservations of. the tiallycarboni'zed coal orseini-coke. 3 i interiorsof retortswhich havev cooled voff subvThe temperatureat which-the coalbecomes sequent toy operation over verving periods. v plastic vvarieswithdifferentwcoalsbut is ordi- 40 From Athe character of the material"found nai-ily' between 700 and 800' E. 51.1111- any event, throughoutthelength 0f .the reifill'` and adherthan-about v850" 11K-and uponfurther heat treate Athe lrielkirlse on theshell we .are able toreconment inthe inclinedrotary retorttne ooaibaus struct to someextentfthey reactions bv 'which are formed. The retort. is externallyheated, coal balls `are made. The conclusions reached the. heating gasesranging in temperat'ur'el from from theseobservations have been. checkedand about. io5o F. at Ione lower efndoi the retort to confirmed by testsmede in revolving retorts with 850 vto 950 F. at the vupper end, suchgases `intermittent operation. s traversing the 'retort' from the lower't'o rthe -Themxture 0fvr nely divided Coal and breeze upperendth'ereof. '1 50]'v charged into the Vretort at about, 600 lli. is,.as f

cipal disadvantages ofthe above mentioned, conveyed bythe revolvingacprocess as carried' out heretofore 'has been the r tionof theinclinedretort` toward the dischargel non-uniformity of the product,which attimes end. Atl'the pointvwiiere the incoming matetaken form'either in balls..whichare too large" 55 perature of the shell is about800 F. The ternperature of the coal mixture is increased as itprogresses until it attains the temperature at which it becomes soft orplastic. Yellow tar vapor is first given of! as it approaches thesoftening temperature. In the dry' state' the feed of coal and breezedoes not stick to\l the steel shell of the retort. 'I'he hot, dry, nnecoal and breeze flows almost as freely as a fluid. Its rate of ilow israpid and the cross section of material is thin and its arc of contactwith the steel shell is small. Because there is thus little tendency'forthe material tov be carried up by the revolving action of the retort,mixing and turning is at a minimum vand segregation is promoted.

At a temperature above 700"v F. the coal softens and gives olfhydrocarbon vapors and distillation has begun. The exact temperature atwhich the coal softens is different for different coals, but the rangeis between 700- and 800 l". Distillation Vreally begins at lowertemperatures. Some hydrocarbon vapors are given offat temperatures below600 F. These vapors are condensable light oils and the vapors are white,whereas the vapors given olf at or about the softening point of the coalare yellow and condense to tar.

As the coal softens it becomes sticlLv. The whole mass does not meltinto a fluid state, but some constituents of the coal soften, wet thesurfaces of adjacent unsoftened or inert particles and bind the wholeinto a loosely coherent mass. In this condition its coeillcient oi'friction on steel is greatly increased. Insteadof a thin layer, looselyflowing, there is a thickening of the bed, because the increase infriction not only retards its ow down the retort but increases thelength of climb up the arc of the revolving shell. The charge haschanged from dry to wet. It is now in the plastic stage. The transitiontakes place quickly, probably in two or three-minutes.

Revolving action of the retort raises the mass and as it falls over itis kneaded and disintegrated into smaller masses, quite irregular inshape and size. The segregationinto small masses; that later becomehardened as coal balls is not dependent on snow balling action; that is,the larger masses are not the result of small pieces rolling down asurface of material and increasingv in size as a snow ball gains in sizeas it rolls down a slope. The size of 'the masses that finally emerge asballs is determined by the agglutinating property of the coal at thetime it reaches its softening temperature in the retort.

Transition from the dry state of the incoming feed, through the plasticstage, to the dry stage of senil-coke is rapid, of the order of 5 to` l0minutes, perhaps for some `coals even less. The semi-Huid mixture istorn apart lby the revolving action of the retort into soft masses thatquickly attain suilicient consistency to be individual pieces. Onlyunder most unusual conditions do two such pieces coalesce or do'we flndone ball rolled within another. Free to move along and out of the way ofoncoming coal, these smaller masses of soft material soon become dryVand solid with roughly spherical shape.

Size and structure of the coal balls are the most important objectivesincontrol of the process.

a prod uct with satisfactory structure will have a volatile mattercontent of between 14 and18%. Experience has shown that for any givencoal (l) 'nie size of the pieces that emerge as low temperature cokeballs is determined by the agglutinating .property of the coal at thetime it reaches its softening temperature in'the retort, and

(2) The structure of the low temperature coke is determined v(a) by thecharacter and proportion-of inerts mixed with the coal and (b) by therate and maximum temperature of heating and the effective control of therates and temperatures in preplastic, plastic and post-plastic ranges.

Proper application of heat to the coal is one ofthe problemsencountered. Coal and low temperature coke are fair insulatingmaterials. Haat transfer is slow under low temperature potential.

In this process the heat forprocessing is applied both'indirectly anddirectly. Indirect application is'through the'steel ducts of the roasterand the shell of the carbonizer. Heat transfer here is ef flcientbecausethe coal is kept inV motion over the steel and because by mixing freshsurfaces are constantlytouching the metal. Thatiathe transfer of heat isemcientso long as the metal is clean. There is nodimculty in keeping themetal clean in roaster and storage apparatus but in the carbonizer,where the atmosphere contains condensable tar vapors, scale` accumulateson the steel and retards heat transfer.

One-factor determining the structureof the coal Iballs is the rate oi'application of heat and the maximum temperature in the carbonizingretort. Sufficient heat must be supplied to the coal f and breezemixture in the carbonizer to raise its temperature to 'about 850 F.Higherv temperatures than this ordinarily simply serve to harden thesurfaces of the balls and ldevelop shrinkage cracks. Unless the materialin process is heated to about 850 F. theproduct will be too high lnvolatile matter content and. too soft to handle .and its shatter indexwill be too low.

It is found that in the prior process coal fed into the upper end of theinclined rotary retort willtraverse the length of theiretort-some 100feet-and be discharged at the lower end in l0 minutes. 'This movement isundesirably fast.

' The coal isnot carbonized to the proper extent.

The desired size of product is a range between one and six toeight'inches in diameter.` The structure should be dense, homogeneousand resistant to shatter. Ash, sulphur -and fusion point of ash aredetermined by the coal used.- The content of volatile matter will dependon the treatment in the retort. .It has been found that While hot it issoft and can be pressed or changed in shape. 'Ihe pieces do not assumethe desired roughly spherical shape." I'he surfaces rof the masses arewrinkled vancl folded. f

The conical outlet of the retort retains a bed of material'the' lengthof whichdepends on the shape and slopefof the retort'. The bed consistsof coke balls'at thelower and deeper end and coal at 4the Vupper endwhere it thins out to the minimum depth. Coal flows down the shell fromthe charging end in a thin stream until it meets vthe tail of the bed.The bed may.' be too long and deep at the lower end and theballs destroythemselves byvlong continual grinding and in fact cut the steel ,of theretort. y u We have discovered that by properly controlling the movementof the coal through the carbonizer the disadvantagesof the prior processmaybe eliminated. The movement of the coal through thecarbonizer may beyregulated so that the coal is properlyvpreheated and vdoes not pile upagainst the coal in the plastic zone. Moreover, the vdepth of the coalin the ball-conditioning zone may be deslrably reduced and the ballslejected at the proper time. 'I'he quality'of the product is superior andthe production of the carof the coal in the plastic nnulal passagewaybonizing unit is increased.

We restrain the movement of the coal along the retort. While this isparticularly'important in thepreheating zone we flnd that advantages arealso obtained by restraining the movement and .ball-conditioning zones.We also find that it is of .advantageto at least partially temporarily'segregate the coal which has not yet reached plastic state from thatwhich has reachedplastic state. Preferably the coal in each of the threezones-the first or .pre-

heating zone, the'second or plastic zoney and the third orball-conditioningv zone--is at least'partially temporarily segregatedduring the process.v

This segregation may be eife'cted by dams in the. i

carbonizer. Such dams, in addition to perform-J ing'theirsegregatingfunction. also perform a re-v straining function to prevent the coalfrom piling up undesirably. The restraining function may also beperformed by other meanssuch as baflies or, as we have termed it,rifling, arranged in various ways in the carbonizer.' At the lower ordischarge end of the carbonizer the balls are preferably dischargedthroughan opening at a higher level than the position of the balls intheI carbonizer adjacent such opening and are ele` 29.' means (notshown) a stationary conduit I8. In-

ing the shell form -no part of the present invention such means are notshown, but it will be understood that the shell is' suitably supportedto permit rotation therewithin of the retort 2. At its opposite ends theshell 8 has seals III which substantially seal the passageway 9.

There is provided-a furnace gases are recirculated through a conduit I5to a fan I8 which discharges the same through a.v conduct Il back intothe furnace II. The .fan I6 `also creates the draft for forcing 'theheating gases from the furnace II into yand through the passageway l9.

i At the upper end of the retortl2 there is positioned and maintained bysuitable 1 supporting .tegral with the retort 2 is an internal skirtporueny is which at its' left hand end, viewing vated from such positionto the level of the opening. This is preferably done by dischargeliftersin the carbonizer. The combined result of the dams,v baiiies .anddischarge lifters is to bring Figure 1, is of the same diameter as theinterior of the retort and welded thereto and atA its right handend isreduced to substantially eifecta seal with the left hand end of theVstationary conduit I8, such seal being designated 20. Thestavtionary-.clmduit I8 is perforated to admit va about a, nicety ofcontrol n the apparatus and y thermal and economic advantages.

f Other details, objects and advantages of the invention will becomeapparent as the following description `of a present preferred embodimentthereof and a present preferred'method of practicingthe same proceeds. i

vIn the accompanying drawing vWe have shown a present preferredembodiment of the invention and a present preferredmethod of practicingthe y same, in which Figure 1 is a diagrammatic central longitudinalYcross-sectional viewthrough an inclined rotary carbonizing retort; and IFigure 2 is a transverse cross-sectional view taken on the line II-II ofFigure .1.

Referring now more particularly to the drawing,4 reference numeral 2designates an inclined rotary carbonizing retort which in its generalshape andy structuremay be of standard design. The retort is designedfor rotation in the direction of the arrow vA in Figure 2, beingAsupported for rotation upon'rollers (cooperating with tires l carriedby the retort. The retort is rotated by a gear 5 carried by a drivingshaft 8 and meshing with-a ring-gear 1 carriedby the retort adjacent itsupper vend. The means for supporting and rotating' they retort are shownpurely diagrammatically and without a showing-of detail because theinvention ydoes not reside therein. Suitable thrust means are providedto prevent the retort from moving longitudinally during rotation.

'I'he retort 2 is inclined as shown so that upon rotation the materialtherein will feed generally downwardly from right to left viewing Figure1 due to gravity. The 'retort is surrounded throughoutthe major portionof its length by a stationaryshell 8 the body of which is of generallycylindrical shape. as is the retort', spaced from the retortsuflivciently to provide an 9 between the retort and the shell. Both theretort and the shell are preferably made of steel.

and isk vcylindrical casing 2I containing a feed screw 22 through whichthe charge ofecoal and breeze is fed into the retort. vThe charge passesinto the n I casing 2| through a conduit 23.v The screw 221s "rotated bya motor 2l.v

The lower or left hand end of the retort 2 may be either sealed or opento the atmosphere. The conduit I8 discharges the hydrocarbon gas issu-'ing from the upper end of the retord through a water chamber 25 and aconduit 26to a suitable gasreservoir. The movement of gas throughtheconduits I8' and 26 maybe and preferably is facilitated by an exhaustfan (not shown).

Most of what has ybeen described above is of more or less standardconstruction. The present invention has to of the charge within Withinthe retort is aplurality of dams 21, 28, 29,

three dams being shown. lalthough the number' thereof may be increasedor decreased. The particular arrangement shown, however, affordsparticular operating advantages. Each of the dams is of generallyfrusta-conical shape and is welded at its periphery to the interior ofthe retort 2. The dams are inclined generally. downwardlyof the retortas shown. They serve to retard or restrain the movement of thechargealong the retortwhereby to insure proper carbonizatlon thereof as aboveexplained. The preheating zone As the means for support- 76 lof abovereferred to extends substantially from the point at which the chargeenters the retort to the dam 21. The plastic zoneextends substantiallyfrom the dam 21 to the dam 28. The ballconditioning zone extendssubstantially from the dam.28 to the dam 29.. The portion of the retortto the left of the dam 28 may be considered as a of theball-conditioning zone as the balls pass from the dam 29'and lthroughthe zone to before they are discharged. The retort is also provided withbailles lor rifling 38. Each of such baffles may conveniently comprise ametal angle having the ends of its legs.

welded to the interior of the retort as shown in Figure 2. The bafflesSI1-are disposed at an angle to the length of the retort so that uponrotation the'retort they exert a restraining force on the Il equippedwithl one or more gasburners I2 for supplying heat do primarily with thecontrol. the inclined rotary retort 2.v

charge tending to retard its downward movement in the retort. Thebailles also serve to promote better mixing of the charge in the retortand to eliminate segregation, as upon rotation of the retort portions ofthe charge are carried up by the baiiles and ultimately fall back intootherportions thereof. The baflles also serve an important function inthe portion of the retort to the left of the dam 28 in relieving theinterior of the retort of the severe abrasive action of the balls. Ithas been found that without the protection of the baiiles the retortadjacent itsloweriend has become worn substantially time.

Discharge lifters 3| are provided at the discharge end of the retort 2,such liftels being in the form of hanged metal plates having the edgesof their webs welded to the interior of the inclined nose 32 of theretort as shown. The flanges 33 cooperate with the webs of the plates sothat upon rotation of the retort the lifters in effect scoop up ballswhich rise above a predetermined level at the lower end of the retortand raise the same to discharge them through an outlet 3l. The thicknessof the bed of balls in the lower end of the retort may be controlled bythe lifters 3|, as those balls which lie below the lowest point whichthe lifters assume during rotation of the retort will not be lifted andejected thereby. The lifters serve an important function in controllingthe discharge of the balls and the depth of the bed at the lower end ofthe retort.

The dams, bailles and lifters cooperate to bring about controlledmovement of the charge through the retort. The depth of the bed ismaintained as desired at all points along the retort and propercarbonization of the charge is insured. Although ballles 30 are shownonly in the zones before and after the plastic zone and not in theplastic zone, bailles may in some instances be provided in that zone orbailies 'may be omitted elsewhere in the carbonizer as the particularconditions may dictate. y The character of the coal used is perhaps themajor factor determining the particular arrangement of dams, bailles andliftthrough in a short ranged. -Also the baflles may assume variousother forms while still accomplishing the desired functions.

While we have shown and described alpresent.

preferred, embodiment of the invention and a present preferred method ofpracticing the same,

tating said heated mixture of coal and breeze in an inclined rotaryretort to form it intoballs and retarding the movement of said mixturealong" the retort sufliciently to cause said mixture to move through theretort at an average speed substantially less than 10 feet per minute sothat it forms into balls of reasonably uniform size for fuel by exertingat successive points along the retort extraneous pressure on surfaces ofsaid mixture other than those surfaces which facer radially outwardlyfrom the axis of the retort.

2. A process. of low temperature carbonization ol''coklng` coal toA formballsl of f semicoke comprising heating to a temperature notsubstantially lo'wervthan about 600 F. and not substantially higher thanabout 800 F. a mixture of coking coal and breeze and tumbling saidheated mixture and advancing the same at an average speed of less than10 feet per minute to reduce the coal tor plastic state and continuingsaid heating, 'tumblingV and advancin to form said mixture into ballsand retarding the advancing movement of said mixture suillciently tocause said mixture to advance at an average speed substantially *lessthan 10 feet per Aminute so that it forms into balls of reasonablyuniform size for fuel by exerting at successive points along the advanceAof said mixture extraneous ,pressure on surfaces of said mixture facinggenof said mixture in said chamber and retarding` the advancing movementof Isaid mixture before it becomes plastic sufficiently to cause saidmixture to move through the retort at an average speed substantiallyless than 10 feet per minute so that it forms -into balls of reasonablyuniform "size yfor fuel by exerting at successive points along theretort extraneous pressure on surfaces of said mixture facing generallyin the direction of advance of said mixture.

4. A process of low temperature carbonization Aof coking coal to fonnballs of semi-coke comprising heating to avtemperature not substantiallylower than about 600 F. and not substantially higher than about 800 F. amixture of coking coal and breeze and tumbling said heated ,mixture andvadvancing the same at an average speed of less than 10 feet per minuteto reduce the coal to plastic state and continuing said` tumblingandvheatingv to lonn the mixture into` balls and atleast partiallytemporarily segregating in the direction of movement 'the tumblingmixture which has not yet lreached plastic state. from that whichhasreached plastic state.

5. A process o1'v lowtemperature carboniza'tion of coking coal to formballs of semi-coke comprising heating to a temperature notysubstantially lower than about 600 F'. and not substantially higherthanabout 800 F. a mixture of coking coal and breeze and tumbling saidheated mixture and advancing the same at an average speed of less than10 feet per minute to preheat said mixture in a first zone and reducethe coal to'plastic stateand continuingl said tumbling and heating toform the coal into balls in a second zone and at least partiallytemporarily segregating in the Adirection of movement the tumblinmixture in said respective zones. Y

6. A process of low temperature carbonization of coking coal to formballs of semi-coke comprising heating to a temperature not substantiallylower than about 600 F. and notjsubstantially higher than about 800 F. amixture of of coking coal 7. A process of low temperature carbonizationof coking coal to form ballsof semi-coke comprising simultaneouslyadvancing, heating to a temperature not substantially lower than about600 F. and not substantially higher than about 800 F. and tumbling abody of coking coal mixed with breeze to reduce the mixture of cokingcoal and breeze to plastic state and thereafter continuing the heatingof'said mixture and advancing and tumbling the same and exertingextraneous pressure at successive points along the retort on surfaces ofsaid'mixturefacing generally in the direction of advance oi said mixturesutliciently to Vcause said mixture to advancev at `an average speedsubstantially less than 10 feet per minute 'so' that said mixture formsinto balls-of reasonably uniform size for fuel.

8. A process `of low temperature carbonization to form balls ofsemi-coke comprising heating the coking coal mixed with breeze to atemperature not substantially lower than about 600 F. and notsubstantially higher than about 800 F.r to plastic state and thereafterforming it into balls by continuing the heating advancing the throughthe retort at an average speed maintaining a layer of substantial depthor balls at the lower end of the retort, elevating the balls inclinedrotary retort whilel opening at a A of less than 10 of thev material inthe retort to discharge the upper portion only of said layer through anhigher level than the position of the balls in the retort adj acent suchopening..

at the lower end of 9. A process of low temperature carbonizaticn` ofcoking coal to form balls of, semi-coke com.- prising heating the cokingcoal mixed with breeze to .a temperature not substantially lower'thanabout 600 F. and notsubstantially higherthan about 800 F. to plasticstate and forming it into balls bycontinuing the heating and tumbling inan inclined Arotary retort while advancing the charge through theretort' at an average speed layer of substantial depth of balls at thelower end of the retort, elevating the balls at the lower end of theretort to discharge the upper portion only of said layer through anopening at a. higher level than the position of the balls in the retortadjacent such opening and regulating the depth the retort adjacent thedischarge opening by said elevation and discharge. Y10. A process of lowtemperature carbonization of coking coal to form balls of semi-cokeVcomprising heating to a temperature not substantially lower than about600 F. andv not substantially higher than'about 800 F. a mixture ofcoking coal and breeze to bring the coal to plastic state and tumblingthe mixture in a retort while advancing the same at an tially less thanl0 feet ,per minute so that it forms into balls, maintaining a layer ofsubstantial depth of balls at the lower end of the retort and regulatingthe depthof the charge at the portion thereof where balls are formed byelevating and discharging only balls rising above the desired level. f

CARL E. LESI-IER. JOHN B. GOODE.

feet per minute', maintaining aV average speed substan-

